1. Field of the Invention
This invention relates to a method and apparatus for dressing a saw blade, in particular an endless belt-saw blade wherein irregularities in surface evenness of the blade are measured.
2. Description of Related Art
The dressing of belt-saw blades usually includes three different tasks. So that a belt-saw blade during its guiding is loaded as uniformly as possible and no extension stresses occur, which may lead to hair-fracture formations or to an untrue sawing of the belt-saw blade, the belt-saw blade on a rear side must be slightly longer than on the tooth side. This is required because the tooth side is exposed to cutting forces which at this side lead to a greater extension than on the rear side. For uniform running it is also necessary to form a so-called tension profile into the belt-saw blade. This tension profile includes an embossing transverse to a longitudinal direction of the belt-saw blade and extends over an entire length of the belt-saw blade. It important for the belt-saw blade to have no dents or bulges.
For eliminating dents and bulges, there is a device which in technical language is described as a dressing center. Such a device uses measuring stations of different types. For measuring the tension profile a measuring station is arranged in a region where the belt-saw blade blends from an arcuate deflection into the level running. This measurement is a measuring line transverse to a movement direction of the belt-saw blade. A second measuring for determining bulges or dents occurs at a measuring point below which the moved belt-saw blade is led through. From a fictive, ideal blade plane, downward deformations, thus dents, or upward deformations, the so-called bulges, are measured. A last measuring station is for the path measurement. Because the tension profile measuring station and the bulge and dent measuring station are not arranged directly at the location of the correction deformation, one must continuously measure when the corresponding deformation is located at the corresponding processing unit. This measuring station includes a roller scanning. The measurements of the deformations may be accomplished optically or with electronic sensors. The corresponding measuring data are delivered to a computer which as a function of variables activates the corresponding machining units.
In this invention, one is interested in the machining unit which is suitable for smoothing bulges or dents. Because the corresponding machining is accomplished using various roller pairs, the corresponding processing unit is also called the roller unit or planing unit.
Such planing units include two pairs of rollers standing vertically over one another, wherein the roller pair which corrects dents has a roller with a convex cross section profile below the belt-saw blade to be corrected and above the belt-saw blade to be dressed has a roller with a concave cross section profile. For correction of bulges these rollers are accordingly arranged in reverse. In this case below the belt-saw blade there is arranged a roller with a concave cross section profile and above the belt-saw blade to be dressed there is arranged a roller with a convex cross section profile.
Devices of this type are known on the market in the most varied of embodiment forms, for example as taught by German Patent Reference DE-A-42 14 784 or PCT International Application WO 97/46335.
Before dressing centers appeared on the market, or also today in small businesses, belt-saw blades were and are dressed manually by highly paid expert workers that shaped the belt-saw blades with a hammer. The dressing centers today function very similarly to the previously mentioned experts which are referred to as xe2x80x9csaw blade doctorsxe2x80x9d. Hydraulic units move two rollers of the roller pairs up and down. Because the belt-saw blade to be dressed is continuously advanced, the rollers must traverse up and down, instantaneously, which causes a correspondingly high emission of noise. The rollers are fed as a function of the measured unevennesses. Simultaneously, the advance is essentially controlled so that pressure is applied proportional to deformation. Because the hydraulic advance depends on many factors such as temperature, viscosity and mechanical tolerances, and because the kinetic energy of the roller movement has an effect, the belt-saw blade is planed in a type of approximation in several repeated cycles. In other words, for each passage of the blade a linear path is measured out and the correction is accomplished. The entire machining unit is displaced relative to the saw blade by a given amount and the correction again takes place. With the devices known today this process must be effected several times over the whole saw blade width, resulting in many passages. Accordingly, the dressing centers known today are very time inefficient and are also very noisy. The precision of the belt-saw blades planed on known dressing centers is practically directly dependent on the dressing time invested therein.
It is one object of the this invention to provide a working method which alleviates the previously mentioned disadvantages.
It is another object of this invention to provide a device which functions according to the new method.
A method and device, each which fulfils the above mentioned objects is described in the claims and the subsequent description.